The Democrat Party won the most seats in parliament in 1948, 1976, and 1992 - however, it has never won an outright parliamentary majority. The party's electoral support bases are Southern Thailand and Bangkok, although election results in Bangkok have fluctuated widely. Since 2004, Democrat candidates won three elections for the governorship of Bangkok. Since 2005, the Democrat Party's leader has been Abhisit Vejjajiva, incumbent opposition leader.

The Thai name of the party, Prachathipat (ประชาธิปัตย์), is a corruption of the word prachathipatai (ประชาธิปไตย) which means democracy, democratic or democrat. The party said it wanted the term to mean the people in whom democracy is vested.[8]

The Democrat Party was founded by Khuang Aphaiwong on April 6, 1946, as a conservative and royalist party, following the January 1946 elections. Early members included royalists opposed to Pridi Phanomyong and former Seri Thai underground resistance members. The party competed against the parties affiliated with Pridi Phanomyong and the Progress Party (Thailand) of brothers Seni and Kukrit Pramoj. In the January 1946 elections, the Pridi-led coalition had won a majority in the Parliament. However, Pridi declined the nomination as prime minister and the parliament appointed Khuang as premier. Khuang resigned in March 1946, after being defeated on a bill, and was replaced by Pridi. The smaller Progress Party later merged with the Democrat Party.

After the death of King Ananda Mahidol in 1946, the Democrat Party accused Pridi of having been the mastermind behind the King's death and spread this propaganda throughout the capital.[9] Seni Pramoj's wife told the US chargé d'affaires that Pridi had the King assassinated, and Democrat Party members spread the same rumor to the British embassy.[10] A few days after the King's death, a Democrat MP yelled out, "Pridi killed the King!" in the middle of a crowded theater.[11]

The palace persuaded Marshal Plaek to appoint Khuang Aphaiwong as figurehead civilian Prime Minister.[12] In subsequent elections on January 29, 1948, the Democrats won the majority for the first time, and reappointed Khuang as Premier. Khuang packed his cabinet with palace allies, much to the consternation of the military. The military later, claiming that they were supporters of constitutional monarchy, demanded that Khuang resign. Marshal Plaek replaced Khuang as Prime Minister.

Although having no representatives in the cabinet, the Democrats had key representatives in the constitution drafting committee. Headed by Seni Pramoj and dominated by royalists under the direction of Prince Rangsit and Prince Dhani, the 1949 Constitution elevated the throne to its most powerful position since the 1932 overthrow of the absolute monarchy.[13] Among its features was a senate whose members were to be appointed directly by the King. The constitution triggered protests among much of the public. It was attacked as contrary to the purpose of the 1932 revolution. Critics were branded republicans and communists.[14]

Subsequent elections saw military-backed parties winning the majority in the House; however the Senate was still dominated by Democrats and other royalists. As Marshal Plaek was still Premier, tensions between the military and the Democrat/palace-alliance steadily increased. On November 29, 1951, the military and the police seized power, just as King Bhumibol's ship was returning to Thai waters. Although the military's 1952 constitution, which was similar to the 1932 Constitution, called for elections, the Democrats had been practically barred from government for the following 23 years.

Sarit Dhanarajata seized power from Marshal Plaek in 1957. Unlike Marshal Plaek, Sarit deified the throne, thus removing any advantage that the Democrats, who had previously been dominated by royalists, may have had. The junta did not immediately abrogate the 1952 Constitution, but instead appointed Pote Sarasin as figurehead civilian Premier. Elections were held on December 15, 1957, resulting in the Democrats losing to military-backed parties. Sarit's ally General Thanom Kittikachorn was appointed as Premier. Sarit later went to the US to seek treatment on his liver cirrhosis. Eight months later, he recovered, returned and executed another coup while dissolving Parliament, abrogating the Constitution, and ruling by Revolutionary Council. For the next 9 years, there were no elections in Thailand, and the Democrat Party had been dormant.

Thanom Kittikachorn, who had succeeded Sarit after his death, was pressured to promulgate a democratic constitution on June 20, 1968, and hold elections in February 1969. Parties affiliated with Thanom won that election, and the Democrats joined the opposition. Thanom, his son Narong, and his brother-in-law Praphas Charusathien became known as the Three Tyrants. They later executed a coup against their own government on November 17, 1971, abrogating the Constitution and running the Kingdom through a National Executive Council. Beginning in 1972, popular demands for democratic freedoms began to grow. In response to the demands, the National Executive Council drafted a new charter in December 1972, which established a wholly appointed 299-member National Legislative Assembly.

Opposition to the Three Tyrants culminated on October 14, 1973, when 400,000 protested at the Democracy Monument. A violent crackdown and subsequent intervention by the King led to the appointment of Privy Councilor Sanya Dhammasakdi as Premier. The Three Tyrants left the Kingdom. Sanya established a constitution drafting committee, consisting of Kukrit Pramoj (who by this time had established and defected to the Social Action Party) and many academics. The new constitution was promulgated on October 7, 1974.

Legislative elections were held in January 1975, resulting in none of the 22 parties coming close to winning a majority. The Democrats, led by Seni Pramoj, formed a coalition government in February 1974. Seni was appointed Premier, but the coalition was unstable, and was replaced in less than a month by a Social Action Party-led coalition which appointed Social Action Party leader Kukrit Pramoj as Premier.

The Kingdom descended into political chaos, with anti-leftist groups growing increasingly violent. In January 1976, the military pressured Kukrit to dissolve Parliament. Elections were scheduled on 14 April. The months leading up to the election were particularly eventful: The head of the Socialist Party was assassinated, the Red Gaur attempted to bomb the headquarters of the New Force Party (a leftist party), and the Chart Thai Party was established with the slogan "Right Kills Left". Seni Pramoj's Democrats won the most seats in the election, and formed an unstable coalition government.

Seni's government came under great pressure. A bill to extend elections to local levels was passed by Parliament 149-19, but the King refused to sign the bill or return it to Parliament, effectively vetoing it.[15] As anti-leftist sentiments escalated, Praphas Charusathien returned shortly from exile and met the King. Students protesting against Praphas' return were attacked by Red Gaur paramilitary units. On September 19, 1976, Thanom also returned from exile and was immediately ordained as a monk at Wat Bovornives. Massive protests erupted. The King and Queen returned from a trip to the South and visited monk Thanom, leading Seni to resign from the premiership in protest. His resignation was refused by Parliament, but initial attempts to reshuffle his cabinet were vetoed by the King.[16] The political tension finally culminated in the 6 October 1976 massacre, when Village Scouts and Red Gaur joined with some military and police to massacre at least 46 students protesting at Thammasat University.[17] That evening, the military seized power and installed hard-line royalist Tanin Kraivixien as Premier.

The military coup to restore order was endorsed by the King, who declared it was "a manifestation of what the people clearly wanted."[18] The new constitution did not express any obligation for the government to have a cabinet or elections, and gave the Premier near-absolute powers.

In 2003, Chuan retired from his position as party leader. Banyat Bantadtan, a southerner and a close aide to Chuan, succeeded him after a closely fought leadership contest with Abhisit Vejjajiva.

Democrat Party 2005 election poster highlighting the "201" campaign

Democrat Party's candidate Apirak Kosayothin won 2004 Bangkok gubernatorial election; the TRT Party did not submit a candidate. The Democrat Party lost further ground to Thai Rak Thai in the 2005 general election. In the election campaign, the Democrats had a populist platform, promoting job creation, universal education and health care, and law and order against crime and corruption.[20] The party aimed to gain 201 seats, enough to launch a vote of a no confidence debate against the premier. They won 96 out of 500 seats and 18.3% of the popular vote. The party's leader Banyat Bantadtan resigned after the election.

On March 6, 2005, Abhisit Vejjajiva was elected the new party leader. Upon succeeding the party's leadership from Banyat, Abhisit noted, "It will take a long time to revive the party because we need to look four years ahead and consider how to stay in the hearts of the people."

The popularity of the populistThai Rak Thai Party in Thai politics from 2001 to 2006 presented new challenges to the Democrat Party. The TRT championed populist policies with its focus on providing affordable and quality health care for all citizens, village-managed microcredit development funds, the government-sponsored One Tambon One Product program, and others. The populist policies earned the TRT enormous support from rural constituencies, unprecedented in Thailand's history.

Opposition to the TRT government rose in Bangkok after Thaksin's family announced their tax-free sale of their 49.6% stake in Shin Corp to Temasek for almost 73.3 billion Baht on January 23, 2006. The People's Alliance for Democracy began a series of anti-government protests. Several Democrat Party leaders also joined the PAD,[21] which accused Thaksin of disloyalty to the throne and asked King Bhumibol to appoint a replacement Prime Minister. Thaksin Shinawatra dissolved the House of Representatives on February 24, 2006 and called for an election. On March 24, 2006, Abhisit Vejjajiva publicly backed the People's Alliance for Democracy's call for a royally-appointed government. Bhumibol, in a speech on 26 April 2006, responded, "Asking for a Royally-appointed prime minister is undemocratic. It is, pardon me, a mess. It is irrational".[22]

Abhisit and his allies of opposition parties boycotted the April 2006 elections, claiming it "diverted public attention" from Thaksin's corruption charges and his sale of Shin Corp.[23] The boycott caused a constitutional crisis, prompting Thaksin to call another round of elections in October 2006, which the Democrats did not boycott. The Army seized power on 19 September and cancelled the upcoming election.

Abhisit voiced displeasure at the 2006 coup that overthrew Thaksin, but otherwise did not protest it or the military junta that ruled Thailand for over a year. A fact-finding panel at the Attorney-General's Office found that the Democrat Party bribed other parties to boycott the 2006 parliamentary election, which forced the constitutional crisis, and voted to dissolve the party. It also found that Thaksin's Thai Rak Thai party bribed other parties to contest the election. A junta tribunal acquitted Abhisit and the Democrats of the vote fraud charges, but convicted and banned the Thai Rak Thai party and its entire executive team.

Despite being banned from politics for five years, Thaksin Shinawatra was popular in his former support bases in the Central, North and North-Eastern Thailand and attempted to maintain an active role in Thai politics by supporting the People's Power Party, which had become the successor party of the banned TRT. Abhisit promoted populist policies in his party's campaign as the Democrat Party's platform in the 2007 parliamentary election. He claimed that while his platform was categorically considered to be populist, it sought to curb inflation while maintaining fiscal soundness, to apply the village-based microcredit development funds used in the Thaksin-led government but do it as part of promoting royalist sufficiency economy policies in rural areas, and to strengthen the country's long-term competitiveness through universal education through high school.

In the junta-administered 2007 parliamentary election, the People's Power Party won the largest share of the vote and formed a six-party coalition government. The Democrats' populist platform was poorly received in the Central, North and North-Eastern regions. The Democrat Party became the opposition as the second-largest party in the House of Representatives.

The People's Alliance for Democracy resurfaced to destabilize the People's Power Government, after having gone into dormancy following the 2006 coup. Several Democrat Party leaders allied themselves with the PAD in the subsequent 2008–2010 Thai political crisis. The PAD organized extended street protests and later led a months-long seizure of Government House, the seat of the Thai government. In November 2008, PAD forces seized and occupied Don Muang Airport and Suvarnabhumi Airport.

The PAD declared that the only person they would accept as Premier was Abhisit of the Democrat Party.[25] Abhisit voiced displeasure at sieges, but did not stop his deputies from their roles in the PAD.[26]

The sieges ended when the Constitutional Court banned the People's Power Party and two of its coalition allies. During the critical period that followed the rulings, it is alleged that Army commander and co-leader of the 2006 coup, General Anupong Paochinda, coerced former PPP MPs, mainly those of the Friends of Newin Group, to endorse a Democrat Party-led coalition, which secured enough parliamentary votes to allow Abhisit to be elected Prime Minister. These MPs, along with MPs of 4 other former PPP-coalition parties, crossed the aisle to endorse a Democrat-led coalition government. In a December 2008 parliamentary session, the Democrat-led coalition government was voted upon, with 235 to 198 votes in favor of Democrat Party leader and candidate for PM Abhisit Vejjajiva.[27][28]

Soon afterward, PAD leader Sondhi Limthongkul was the target of an unsuccessful assassination attempt. Both Sondhi's son and Thaksin claimed that factions within the Democrat government were behind the assassination; however, Abhisit's foreign Minister claimed that Thaksin was behind it.[30][31][32]

Abhisit dissolved Parliament in early 2011 and scheduled general elections on 3 July 2011. Abhisit unveiled a slate of candidates highlighted by 30 celebrities and heirs of political families, including Chitpas Bhirombhakdi, heiress of the Singha Beer fortune and former staff member of Abhisit's secretariat office.[33] Abhisit promised to increase the minimum wage by 25% if the Democrat Party won the election.[34]

At the general election on 3 July 2011, the Democrats were only able to defend 159 seats in the House of Representatives, while rivaling Pheu Thai Party led by Yingluck Shinawatra won an outright majority. The next day, Abhisit stepped down as the party's leader.[35] However, on 6 August, he was re-elected as the leader of the Democrat Party with the support of 96% of those eligible to vote at the party's assembly - some 330 people including local branch leaders and MPs.[36]